1. Field of the Invention
The present invention relates to a distance measuring apparatus which automatically measures a distance to an object.
2. Related Background Art
As distance measuring apparatuses, a distance measuring apparatus of an active method and a distance measuring apparatus of a passive method have been known. The active and passive methods are types of trigonometric distance measurement methods. In the active method, light is irradiated on an object from an infrared-emitting diode or the like, and the incident position of the reflected light is detected by a linear light-receiving portion such as a divided photodiode or a PSD (position-detecting semiconductor device) to calculate the distance to the object on the basis of the incident position of the reflected light. On the other hand, in the passive method, no light is irradiated on the object. Instead of this, the reflected light of natural light by the object is received by two linear sensors to calculate the distance to the object on the basis of a phase difference between outputs from the respective linear sensors.
In the distance measuring apparatus of the active method, since light is irradiated on the object, the distance can be advantageously measured even at a dark place. To the contrary, when the luminance of the object is higher than that of the irradiation light, the distance measuring apparatus cannot properly receive the reflected light, and a situation may be caused in which the distance measurement becomes impossible or a high distance measurement accuracy cannot be obtained. On the other hand, the distance measuring apparatus of the passive method advantageously requires no light source for emitting irradiation light. To the contrary, when the luminance of the object is low or the object is of a low contrast, the phase difference is difficult to detect, and a situation may be caused in which the distance measurement becomes impossible or a high distance measurement accuracy cannot be obtained. In this manner, the respective distance measurement methods have merits and demerits.